Recovery of glue from chrome tanned leather



Patented Jan. 18, 1944 RECOVER-Y 0F GLUE FROM CHROME TANNED LEATHERAlbert Hoeren, Kitchener, Ontario, Canada, as-

Lime and Alabastine, Canada, Limited, Toronto, Ontario, Canada signor toGypsum,

No Drawing. Application February 12, 1941, Serial No. 378,693

3 Claims.

This invention relates to the treatment of chrome tanned leather in themanufacture of glue and more particularly to a preparatory treatment towhich the leather is subjected to remove the chrome tanning salts andleave the leather in condition for the extraction of glue.

The detanning of chrome leather and chrome leather scrap is an old art,but known methods are slow and wasteful of the glue-yielding material ofthe leather.

The object of the present invention is to provide an improved method,which requires that the leather remain under treatment for a shorterperiod of time which conserves the collagen in the leather and insures asubstantially larger yield of glue or gelatine, and which permits theproduction from such leather of a high grade glue or gelatinesubstantially equivalent to that produced from the best grade of hidesor glue-stock.

In carrying out the invention chrome tanned leather is treated with anaqueous alkaline solution to which is added boric acid or water solubleboron salts, followed by the usual acid treatment. The presence of theboron salts substantially reduces the time of this treatment thusavoiding excessive swelling of the leather, and so conserving thecollagen in the leather. Lime is the economically preferred alkali butthe hydroxides of any of the alkali or alkaline earth groups may beemployed and sodium borate is the preferred addition agent. The amountof borate used is 2.5 to 4% of the weight of the leather. Dry leatherrequires. more than that having high moisture content. Heating is notnecessary as the reactions involved proceed at normal plant temperi.

atures. When the reaction is complete the treating solution is removedand the leather is Washed with Water until it is substantially neutral.It is then treated with a mineral acid, preferably sulphuric, washed andrendered neutral or slightly alkaline by the addition of lime or otheralkali. It is found that when the leather is subjected to thepreliminary treatment described, a l to 2% solution of acid is all thatis required and thus considerable saving in acid is fiected.

The method is illustrated in more detail by the following example:

7000 lbs. chrome tanned leather cut into pieces of suitable size aretreated in an ordinary glue stock washer with an aqueous solutioncontaining 600 lbs. of hydrated lime and 250 lbs. of sodium borate.Sufiicient water is used to submerge the leather. After two or threedays the solution is removed and the stock is well washed with wateruntil the wash water appears substantially neutral. The stock is treatedin an agitating tank for about 4 to 16 hours, depending on the thicknessof the leather, with a 1 to 2% solution of sulphuric acid. The acidsolution should uniformly penetrate the leather. The solution is removedand the stock washed with water to remove remaining acid. This treatmentthoroughly removes the tanning reagents without destroying or removingcollagen and leaves the leather in condition to yield a maximum quantityof glue of high viscosity and good quality under the usual standardmethods of glue extraction from leather.

Chrome splits treated by this method have given a glue yield of about56% in terms of water free stock. The glue has a viscosity as high as130 and is equivalent in quality to that made from best grade hides orglue-stock. In sheet form the glue or gelatine may be clear andtransparent.

The method is applicable to any chrome tanned leather suitable for themanufacture of glue. The leather may be first treated with lime andthereafter with the borate but it is more economical to use themtogether in a unitary treatment. The boron salts greatly facilitate theremoval of the chrome tanning agent and weaker acid solution isrequired. The time of treatment is reduced with less swelling of theleather and less loss of the collagen. This results in the higher yieldof gelatine or glue and the improved quality appears to be due to themore effective removal of the tanning agent.

I claim:

1. In the treatment of chrome tanned leather for the production of glueor gelatine, the method which comprises subjecting the leather to theaction of an aqueous solution comprising an hydroxide selected from thegroup consisting of the alkali and alkali earth metal hydroxides towhich has been added a compound selected from the group consisting ofboric acid and its soluble salts.

2. A method of treating chrome tanned leather for the production of glueor gelatine, which comprises treating the leather with an aqueoussolution of lime to which has been added a compound selected from thegroup consisting of boric acid and its soluble salts.

3. A method as set forth in claim 2 wherein the so treated leather iswashed, treated with a mineral acid, again washed and rendered neutral.

4. A method of treating chrome tanned leather for the production of glueor gelatine which comprises immersing the leather in a solution of limeto Which has been added sodium borate in the proportion of substantially2.5 to 4% of the dry weight of the leather.

5. A method as set forth in claim 4 wherein the so treated leather istreated with a weak solution of sulphuric acid and thereafter washed.

6. A method of treating chrome tanned leather for the production of glueor gelatine whichcomprises immersing the leather in an alkaline solutionand thereafter treating the leather with an aqueous solution of one ofthe group consisting of boric acid and its soluble salts.

7. A method as set forth in claim 1 wherein the so treated leather issubjected to a- 1 to 2% solution of sulphuric acid and thereafter washedwith Water.

8. In the treatment of chrome tanned leather for the production of glueor gelatine, the method which comprises subjecting the leather to theaction of a hydroxide selected from the group consisting of the alkaliand alkali earth metal hydroxides and a compound selected from the groupconsisting of boric acid and its soluble salts in aqueous solution, thesaid compound of the last mentioned group being present in aqueoussolution in the proportion of substantially 2.5 to 4% of the Weight ofthe leather.

ALBERT HOEREN.

